1. Field
One embodiment of the invention relates to a storage medium such as an optical disk, a reproducing method, and a recording method of the storage medium capable of recording and reproducing information with a laser light beam having a short wavelength such as a blue laser light beam.
2. Description of the Related Art
As is well known, in recent years, with prevalence of personal computers or the like, media for accumulating digital data has been increasingly important. For example, currently, an information storage medium capable of digitally recording and reproducing video image information and voice information or the like for a long time is prevalent. In addition, an information storage medium for digital recording and reproduction is used for a mobile device such as a cellular phone.
As an information storage medium of this type, there is often utilized a medium of disk shape because the medium has a large capacity of recording information; has random access performance capable of speedily making a search for desired recording information; and moreover, the medium is small in size and light in weight, excellent in storage property and portability, and is inexpensive.
In addition, as an information storage medium of such a disk shape, currently, there is mainly used a so called optical disk capable of recording and reproducing information in a non-contact manner by irradiating a laser light beam. This optical disk primarily conforms to a CD (Compact Disk) standard or a DVD (Digital Versatile Disk) standard, and is compatible with both of these standards.
There are three types of optical disks, i.e., a read-only type which cannot record information such as a CD-DA (Digital Audio), a CD-ROM (Read-Only Memory), a DVD-V (Video), or a DVD-ROM and the like; a write-once type capable of recording information only once such as a CD-R (Recordable) or a DVD-R and the like; and a rewritable type capable of rewriting information any times such as a CD-RW (Rewritable) or a DVD-RW and the like.
Among them, as a recordable disk, a write-once type optical disk using an organic dye for a recording layer is the most prevalent because of its low manufacturing cost. This is because, if an information recording capacity exceeds 700 MB (Mega Bytes), there is almost no need for erasing recorded information and rewriting new information, and eventually only one recording suffices.
In the write-once type optical disk using the organic dye for the recording layer, after a recording area (track) specified by a groove is irradiated with a laser light beam and a resin substrate is excessively heated to its glass transition point Tg or more, an organic dye film in the groove causes an opto-chemical reaction and produces a negative pressure. As a result, the resin substrate is deformed in the groove. A recording mark is formed by utilizing this deformation.
A typical organic dye used for a CD-R whose wavelength of a recording and reproducing laser light beam is about 780 nm includes a phthalocyanine based dye such as IRGAPHOR Ultragreen MX available from Ciba Speciality Chemicals. In addition, a typical organic dye used for a DVD-R whose wavelength of a recording and reproducing laser light beam is about 650 nm includes an azo metal complex based dye available from Mitsubishi Kagaku Media Co., Ltd.
In the meantime, in comparison with a current optical disk, in a next generation optical disk which achieves recording and reproduction with higher density and higher performance, a blue laser light beam whose wavelength is short at about 405 nm is used as a recording and reproducing laser light beam. However, an organic dye material capable of obtaining practically sufficient recording and reproducing characteristics by using a light beam having such a short wavelength has not been developed yet.
In document 1 (Jpn. Pat. Appln. KOKAI Publication No. 2002-74740), there is disclosed an optical storage medium having a longer wavelength than a wavelength of a write light beam in absorption extremity of an organic dye compound contained in a recording layer. However, in this document 1, for example, there is nowhere described a configuration of enhancing performance of an optical disk itself such as durability in the case where a mark recorded in an optical disk has been continuously reproduced by a blue laser light pickup. There is a need for a signal not to be degraded in the case where a certain track is continuously reproduced. A write-once type optical disk using an excellent dye in reproduction light stability must be provided.
In document 2 (Jpn. Pat. Appln. KOKAI Publication No. 2004-139712), there is disclosed an Ag-group alloy reflection film or a semipermeable reflection film for an optical information recording medium, the Ag-group alloy reflection film being made of an Ag-group alloy containing 0.005 at % to 0.40 at % of Bi and/or Sb in total. However, document 2 merely discloses a reflection film simplex, and does not describe how an organic dye component is used as a recording layer and how the above-described storage medium is configured as using a recording and reproducing light beam having a short wavelength.
As has been described above, a conventional storage medium using an organic dye material is not sufficient in reproduction durability count.